Brief Summary of the Invention
A multilayer ZnO polycrystalline diode that protects against electrostatic discharges, over-current, and voltage surges overcoming the aforementioned drawbacks is provided. The present invention further includes a polycrystalline system formed by a network of elementary ZnO diodes; each elementary ZnO diode comprises at least one ZnO grain and a balance layer of Bi.sub.2 O.sub.3. The balance layer of Bi.sub.2 O.sub.3 is configured surrounding the at least one ZnO grain and the polycrystalline system is formed into a plurality of layers.